Herein disclosed are imaging members useful in electrostatographic apparatuses, including printers, copiers, other reproductive devices, and digital apparatuses. Some specific embodiments are directed to imaging members that have a polycarbonate binder with a specific configuration dispersed or contained in one or more layers of the imaging member. The polycarbonate used as the binder has a relatively high molecular weight and possesses solubility in specific solvents to impart uniform coatings and mechanical robustness. In addition, the polycarbonate may provide an imaging member with longer life and reduced marring, scratching, abrasion and wearing of the surface. Thus, incorporation of the polycarbonate binder into one or more layers of the imaging member provides for increased mechanical strength and improved wear to the imaging member.
In electrostatographic reproducing apparatuses, including digital, image on image, and contact electrostatic printing apparatuses, a light image of an original to be copied is typically recorded in the form of an electrostatic latent image upon a imaging member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and pigment particles, or toner. Electrophotographic imaging members may include imaging members (photoreceptors) which are commonly utilized in electrophotographic (xerographic) processes, in either a flexible belt or a rigid drum configuration. Other members may include flexible intermediate transfer belts that are seamless or seamed, and usually formed by cutting a rectangular sheet from a web, overlapping opposite ends, and welding the overlapped ends together to form a welded seam. These electrophotographic imaging members comprise a photoconductive layer comprising a single layer or composite layers.
The term “electrostatographic” is generally used interchangeably with the term “electrophotographic.” In addition, the terms “charge blocking layer” and “blocking layer” are generally used interchangeably with the phrase “undercoat layer.”
One type of composite photoconductive layer used in xerography is illustrated in U.S. Pat. No. 4,265,990 which describes a imaging member having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer (CTL). Generally, where the two electrically operative layers are supported on a conductive layer, the photoconductive layer is sandwiched between a contiguous CTL and the supporting conductive layer. Alternatively, the CTL may be sandwiched between the supporting electrode and a photoconductive layer. Imaging members having at least two electrically operative layers, as disclosed above, provide excellent electrostatic latent images when charged in the dark with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely divided electroscopic marking particles. The resulting toner image is usually transferred to a suitable receiving member such as paper or to an intermediate transfer member which thereafter transfers the image to a member such as paper.
In the case where the charge-generating layer (CGL) is sandwiched between the CTL and the electrically conducting layer, the outer surface of the CTL is charged negatively and the conductive layer is charged positively. The CGL then should be capable of generating electron hole pair when exposed image wise and inject only the holes through the CTL. In the alternate case when the CTL is sandwiched between the CGL and the conductive layer, the outer surface of CGL layer is charged positively while conductive layer is charged negatively and the holes are injected through from the CGL to the CTL. The CTL should be able to transport the holes with as little trapping of charge as possible. In flexible web like imaging member the charge conductive layer may be a thin coating of metal on a thin layer of thermoplastic resin.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, however, degradation of image quality was encountered during extended cycling. The complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on imaging members. For example, the numerous layers used in many modern photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered imaging member that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, an optional blocking layer, an optional adhesive layer, a CGL, a CTL and a conductive ground strip layer adjacent to one edge of the imaging layers, and an optional overcoat layer adjacent to another edge of the imaging layers. Such an imaging member may further comprise an anti-curl back coating layer on the side of the substrate opposite the side carrying the conductive layer, support layer, blocking layer, adhesive layer, CGL, CTL and other layers.
In a typical machine design, a flexible imaging member belt is mounted over and around a belt support module comprising numbers of belt support rollers, such that the top outermost charge transport layer is exposed to all electrophotographic imaging subsystems interactions. Under a normal machine imaging function condition, the top exposed charge transport layer surface of the flexible imaging member belt is constantly subjected to physical/mechanical/electrical/chemical species actions against the mechanical sliding actions of cleaning blade and cleaning brush, electrical charging devices, corona effluents exposure, developer components, image formation toner particles, hard carrier particles, receiving paper, and the like during dynamic belt cyclic motion. These machine subsystem interactions against the surface of the charge transport layer have been found to consequently cause surface contamination, scratching, abrasion-all of which can lead to rapid charge transport layer surface wear problems. Thus, a major factor limiting imaging member life in copiers and printers, is wear and how wear affects the multiple layers of the imaging member. For example, the durability of the charge transport, overcoat and anti-curl back coating (ACBC) layers, and the ability of these layers to resist wear, will greatly impact the imaging member life.
Binders of a weight that fall within a critical molecular weight range are used in current imaging members. These binders require a high molecular range so that the desired viscosity can be achieved. The viscosity level imparts high quality coating for the imaging member layers and is critical for long mechanical flexing life. Generally, uneven thickness in the layers of the photoreceptive material of the imaging member results in performance degradation of the belt. Accordingly, it is desired that each layer have a substantially uniform thickness across the web. Without these binders, the layers of the imaging member will have uneven thickness and substantially lower wear resistance, thus decreasing the overall life and operability of the imaging member. In addition, because certain layers of the imaging member, such as for example, the charge transport layer, the anti-curl back coating layer and the ground strip layer, can greatly impact the mechanical life of the imaging member, incorporation of the binder into such layers are desirable to increase quality and life.
The charge transport layer is a photoconductive layer that photogenerates holes and injects the photogenerated holes into an adjacent layer. The charge transport layer may also be known as a “small molecule transport layer.” The small molecule dispersed in the charge transport layer help facilitate the charge transport through the layer which is important as this layer is used to maintain electron movement and prevent electrostatic charge buildup.
The ground strip layer is applied to one edge of the imaging member. Inclusion of this layer helps to promote electrical continuity with the other layers, such as the conductive layer through the hole-blocking layer.
In the production of multilayered imaging members, the drying/cooling process used to form the layers will often cause upward curling of the multiple layers. This upward curling is a consequence of thermal contraction mismatch between the CTL and the substrate support. Curling of a imaging member web is undesirable because it hinders fabrication of the web into cut sheets and subsequent welding into a belt. To offset the curling, an anti-curl back coating is applied to the backside of the flexible substrate support, opposite to the side having the charge transport layer, to render the imaging member web stock with desired flatness.
Thus, the above layers can greatly affect imaging member life but can also each act as a limiting factor if not made with specific materials. As such, incorporation of these binders into the above layers, are very important for the quality of current imaging members. However, the conventional binder commonly incorporated in the imaging members are no longer being manufactured and present supplies will being running out. Therefore, there is a need for an alternative and cost-effective binder for use with current imaging members to impart wear resistance and good coating qualities that may maintain mechanical life.